Integrated circuits can be formed on semiconductor substrates, particularly silicon wafers, by the sequential deposition of conductive, semiconductive and insulative layers on the wafer. Circuitry features can be etched on after each layer is deposited. After a series of layers have been deposited and etched, the uppermost surface of the substrate can become increasingly non-planar. Non-planar surfaces can cause problems in the photolithographic steps of the integrated circuit fabrication process. As such, it is necessary to periodically planarize the semiconductor substrate surface.
Damascene is a process in which interconnecting metal lines are formed by isolating dielectrics. In damascening, an interconnecting pattern is first lithographically defined in the layer of dielectric, and then metal is deposited to fill in the resulting trenches. Excess metal can be removed by chemical-mechanical polishing (planarization). Chemical-mechanical polishing (CMP), also called chemical-mechanical planarization, refers to a method of removing layers of solid through chemical-mechanical polishing carried out for the purpose of surface planarization and definition of the metal interconnecting pattern. Dual damascene is a modified version of the damascene process that is used to form metal interconnecting geometry using a CMP process instead of metal etching. In dual damascene, two interlayer dielectric patterning steps and one CMP step create a pattern that would otherwise require two patterning steps and two metal CMP steps when using a conventional damascene process.
In a typical CMP operation, a rotating polishing pad, which receives a chemically reactive slurry, is used to polish the outermost surface of the substrate. The substrate is positioned over the polishing pad and is held in place by a retaining ring. Typically the substrate and retaining ring are mounted on a carrier or polishing head. A controlled force is exerted on the substrate by the carrier head to press the substrate against the polishing pad. The movement of the polishing pad across the surface of the substrate causes material to be chemically and mechanically removed from the face of the substrate.
The machinery used to perform CMP is highly sophisticated, with equipment costing millions of dollars. Nevertheless, there are some components of the equipment that require frequent replacement during the polishing operation that contribute significantly to the high costs of CMP. One of these components is the retaining ring, which serves to contain and position the wafer as it is being planarized. As such, it is important to minimize the cost and time to manufacture retaining rings, and to maximize the durability of such rings as well as the ease with which they can be replaced.